How hot is too hot? How hot does bath water need to be before it can burn you? What is a high, but still safe temperature to use?

Some like it hot but. This depends on how long you stay in the water. Water of 127 or above scalds quickly. 120 is the usual upper limit of safe temperature but that could be hazardous if one is in it for 5 minutes. If you are going to be in the water more than a few minutes I would avoid temps above 108 or so, but even that can put stress on your body by raising heart rate.
As. As opposed to a specific temperature, it is more of a combination of time and temperature that will cause burns. What I mean by this is that water at 120 degrees f will burn you eventually, but it will take minutes. But water at 140 degrees f will only need to be in contact with your skin for a few seconds to cause burns. By the time water is 160 degrees f, it will burn you in under a second. Most authorities recommend setting your water temperature to 120 degrees for safety, but many people prefer it to be warmer. If you have children in the house, or people with "neuropathy, " a medical problem (usually due to diabetes, but has many other causes), then you should keep the water set to 120 degrees f. If only healthy adults (who can quickly and reflexively get out of the water if it is too hot) will be using the water, then 130 degrees is fairly safe.